Because of chemical inertness, low allergenic properties, high tensile strength and low melting point, polyolefin fiber and filaments, such as polypropylene are favored candidates for producing a variety of commercial products.
In attempting to apply existing technology and material to meet competitive marketing needs, however, it is sometimes found that the cost and technical problems which arise far exceed the marketing advantages gained.
By way of example, nonwoven material used as cover sheets for diapers, sanitary napkins, as well as covering material for numerous other purposes must generally be cost competitive and retain substantial cross directional (CD) strength and energy (toughness) as well surface softness.
Unfortunately, however, such properties are rarely compatible among nonwovens from synthetic fibers.
In particular, softness is usually gained in such material at the expense of lowered cross directional (CD) strength, and at a substantial increase in cost, figured on a Spun Weight/Time basis.
While the cross directional strength of such materials can usually be increased by increasing the bonding area and/ or number of bonding loci, this also is generally obtained at the expense of material softness and feel.
In effect, therefore, the resulting nonwoven product represents a deliberate compromise, in which particular desirable characteristics are maximized and certain undesirable characteristics minimized, if possible, and accepted in exchange.
In the case of personal contact products such as diaper cover stock and for numerous other covering purposes, it is also found desirable to satisfy certain non-junctional esthetic properties, such as increased opacity (preferably 32%-45%) and stain-masking ability to enhance marketability. In order to accomplish such further improvement, however, the difficulty in obtaining an acceptable compromise or balance in properties is greatly increased.
Generally, staining and opacity problems in synthetic nonwovens have been catagorized and treated in the art as unresolved coloring problems, which have been greatly complicated by the chemically inert nature of polyolefins such as polypropylene. For this reason, colorants and brighteners are preferably introduced as spun melt components. This, in turn, has raised additional problems with respect to leaching, allergenic properties, CD strength loss, smaller spin quench windows, increased cost and the like.
It is an object of the present invention to increase the opacity of polyolefin-containing nonwoven material obtained from at least one web, without raising such added problems.
It is also an object of the present invention to minimize or avoid the need for high concentrations of colorants in synthetic nonwoven material to increase the opacity thereof.